Electron discharge device



March 21, 1933. M. A. ACHESON ELECTRON DISCHARGE DEVICE Filed July 2, 1928 Inventor: TTlarcus A. Acheson.

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His Attorney Patented Mar. 21, 1933 UNITED STATES PATENT OFFICE move A. ACKESON, OI SGHENECTADY, NEW YORK, 'ASSIGNOB TO GENERAL ELECTBI comm, A CORPORATION OF NEW YORK ELECTRON DISCHARGE DEVICE Application filed July 2, 1928. Serial No. 289,688.

.The present invention relates to electron discharge devices of the power type and in particular todevices especially adapted for use with short wavegenerating and amplifying apparatus.

In large power transmitters which generate or amplify oscillations and which employ an electron source in the form of a heated filament, an electrostatic control member and an anode, it is found that after continued use at exceedingly high orders of frequency, various parts of the glass exhibit minor fractures, fissures or other impairments of a disintegrating or deteriorating nature which in the course of time give rise to localized burn-outs and in aggravated cases to a partial collapse of various glass parts and of the electrode structure which they support. These fractures are found for the most part in the neighborhood of the grid support from which they appear to extend along the reentrant or skirt portion of the envelope predominantly in a direction parallel to the major axis of the device. While various theories may be advanced to account for the failure in the glass at these places, I believe that it is due to a strain on the glass particles with attendant fusing, resulting from the presence of high frequency currents induced in the glass. These high frequency currents have their inception in the grid clamp memberwhich constitutes a source of high frequency electrostatic force. The frequency in the case of short wave transmission may attain values as high as 5 X 10 cycles per second (6 meters), resulting in currents which serve to heat the material to excessively high temperatures. The deleterious effects of the induced currents appear to be a progressive or cumulative action having its inception in the slight warming of the glass surface by heat derived from various sources within the envelope which warming effect renders the metallic salts of the vitreous envelope slightly conductive. High temperature glass which ordinarily consists of Pyrex so-called, contains a substantial amount of lead, sodium or other constituents having particles so arranged that in a cold state they offer considerable resistance to current flow but upon being heated, the resistance is sub-' .already present in the glass with the result that the current loss is further enhanced, and so on, until finally the weakest parts of the glass give way. While the impairment is particularly pronounced and especially harmful in the generation of the highest frequency waves, its effect is still appreciable in corresponding degree down to the lowest order of radio frequencies.

I have discovered, in accordance with the present invention, that if a metallic member be placed near the portion of the glass structure in which the breaks occur and is maintained preferably at the same potential as the grid or substantially so, the fissures or fractures may be entirely eliminated. Satisfactory results are also obtainable when the shield is maintained at cathode potential although, as stated hereinbefore, it is considered preferable to charge the metallic member to the same potential as the control member. While I do not wish to be limited to any particular theory or belief, I accredit the fracture fissure inhibiting effect of the metallic plate to its heat shielding property which keeps the adjacent glass surfaces relatively cool thus preventing the initial heating and subsequent development of large current phenomena. It is also possible that the electrostatic effect of the metallic plate or shield may enhance this desirable result. Regardless of the real function of the plate or the manner in which it cooperates either with the envelope or control member or both, I have found that the shield is extremely beneficial in devices of this character. present invention is to be sharply distinguished from the case Where heat shields are provided merely to prevent the temperature at particularly vulnerable parts of the device, e. g., seals and the like, from rising to values greater than the fusing point of the material of which the part is composed. The problems solved by the prior art are concerned usually with direct current and there are no induced currents involved, certainly The tor and amplifier devices. Other objects and features will be apparent as the specification is perused in connection with the accompanying drawing in which corresponding elements are represented by the same reference characters throughout the several views.

' Fig. 1 is an elevational view partly broken away in section, showing a customary type of short wave transmitting device equipped with the metallic shield forming the subject of the present invention; Fig. 2 is an enlarged View in perspective of that portion of the reentrant stem from which the grid is supported, also illustrating the correlated parts, including the shield; Fig. 3 is a high frequency transmitter oscillating circuit including the improved device shown in diagram.

Referring to Fig. 1, there is illustrated a highly evacuated container of elongated shape comprising an envelope 1 made of suitable material, for example, Pyrex glass, a metallic anode 2 closed at one end and adapted to be water cooled and an intermediate metal sealing cone 3 fused to the envelope in the usual manner. Attached to the envelope is a reentrant member which terminates in each of a press 4 and a concentrically mounted hollow cylindrical skirt portion 5 having its lower edge 6 spun inwardly toward the center of the tube as seen more clearly in Fig. 2. About the skirt portion, there is a clamp member 7 to which rigid stay wires 8 are welded for supporting within the anode 2 a grid structure 9 of any suitable design. The stay wires may be secured together if desired in a direction transversely of the tube by two concentrically mounted ring-shaped members 10, 10 the lower of which carries a suitable form of grid framework. For an electron source there is provided a V-shaped filamentary member 11 positioned centrally within the grid electrode by means of two axially aligned rods 12, 12 which are secured in the press 4. As is usual in this form of device, there is provided a combined electrostatic and a heat shielding member 13 in the form of a funnel; this member is snugly fitted within the interior of the anode and held therein by friction. The purpose of member 13 is to protect the seal between the metal cone 3 and the glass envelope 1 from radiated heat and deleterious electrostatic char 'es which ordinarily would collect on the interior surface of the envelope. For energizing the cathode, filament loads 14 are taken through the upper portion of the envelope. In order to remove as far as possible the grid leading-in wire 15 from each of the anode and cathode leads a side arm 16 is provided intermediate the length of the envelope 1, the grid lead being supported therein. For manufacturing reasons, it is considered preferable to have a flexible connection 17 between the horizontal grid lead and the grid clamp.

In accordance with the present invention, there is also provided a concentrically mounted shield 18, shown more clearly in Fig. 2, made of refractory metal, for example, molybdenum and secured in any suitable manner to the grid stay wires in close proximity to the lower or spun end 6 of the longitudinally extending skirt portion 5. The shield is preferably made in the form of a flat Washer or ring, of approximately stock with lugs prOJecting from the outer periphery. Thes lugs may be bent downwardly to offer facility of strapping to the grid stay wires by means of a flexible wire binder 19. The larger diameter of the shield preferably should be not less than the diameter of the skirt portion; the diametral width of the material preferably should be sufiicient to completely cover the spun portion 6. It is obvious that the sheild member may be readily punched and bent to form, thus cheaply made, the only hand work necessary being that of applying the binding;

wires. While in the form of tube illustrated, it is considered preferable to attach the shield member to the grid stay wires, it is evident that in alternative forms of electrode arrangement, the filament supporting rods or even the leads themselves may offer a more convenient surface about which to strap the shield, having due regard for preventing short circuit between such leads.

During operation, it has been found that in the absence of the ring shield referred to, the skirt portion of the reentrant glass member between the grid clamp 7 and the spun end 6 is subject to burn-out or other form of glass failure or disintegration which usually begins with small fisures, subsequently leading to larger openings in the glass. However, with the shield present, these failures were found to be entirely absent even after long continued use of the device operating either as an oscillator or an amplifier of high frequency oscillations. I believe the impairment results from the fact that the metallic salts contained in the envelope material, which in the case of Pyrex is composed of a substantial quantity of lead sodium and other constituents, giving rise to induced currents when the tube is generating, amplifying or simply transmitting high uen oscillations; these currents serve to heat the glass material to a fusing temperature. The problem is of course aggravated by reason of the fact that a device of this character accommodates relatively large amounts of ener the plate voltage being in some cases of t e order of 15,000 with 5,000 volts on the 1d and an output current of approximate y 2 am eres, 30 k. w. input and approximately 20 w. output. The filament energy is also quite large, in the neighorhood of approximately 1 w. in the case of a certain type of device in which the shield has been use most successfully. The ring shield apparently operates to cast a heat and possibly an electrostatic shadow which prevents the lass skirt portion of tubes operating under igh power, high frequency conditions from assuming dangerously high temperatures and strains but whatever be the correct theory involved, I have noted that the shield 18 functions most effectively to remove the cause of this source of tube failure.

In Fig. 3, there is shown diagrammatically one form of oscillation generating and transmitting system in which the improved tube finds utility and in which the tube, in the absence of the metallic shield referred to, would be subject to burn-out. The filament, control and plate members contained in the envelope 21 correspond to those described in connection with Fig.1. The filament is supplied with alternating current throu h transformer 22, a mid-tap being taken rom the secondary to the negative side of the direct current plate supply, as shown. Between the tap and each of the filament leads there is a radio frequency condenser 23, 23 and in the leads themselves, are two radio frequency chokes 24, 24. The control or grid member 9 is connected to the negative bus through a single turn inductance 25, a radio frequency choke 26 and a rid leak resistor 27. The plate or anode mem r 2 is connected to the positive side of the direct current supply, also through a single turn inductance 28 and a radio frequency choke 29. A variable condenser 30 is shown connected between the grid and plate leads at positions intermediate the inductances 25, 28 and the radio frequency chokes 26,. 29 respectively. The condenser indicated by dotted line represents the internal capacity existing between the grid and plate electrodes. One side of the load circuit may comprise the antenna 31 connected to the plate 2 through a fixed condenser 3-2 and the other side may consist of a ground connection to the negative bus. It is evident that with proper values assigned to the various elements shown includng the tube constants, oscillating currents will be set up and transferred to the outgoing line. By adjusting the variable condenser it is possible to obtain electrical waves having exceedingly short wave length,\for example in the neighborhood of 5 or 6 meters wh1ch are particularly suitable for long distance radio transmission. It has been found that when generating current undulations of this character the tube must be equipped with the shield referred to hereinbefore in order to preserve the glass near the grid clamp from crackin or melting and thus to maintain a relative y long tube operating life. It is evident that in case the tube is not a generator of self-sustained oscillations but simply functions to transmit or amplify oscillations developed elsewhere, the use of the shield is also advantageous in preventing the oscillations which are transmitted, with or without amplification, from deleteriously affecting the various ortions of the glass structure in recisely t e same manner as is described wit respect to the oscillator shown.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In an oscillation generator, an evacuated envelope composed of a material which upon being heated conducts current to an appreciable extent, said envelope containing an electron emitting cathode, a control member and an anode, and having a reentrant portion, a clamping device surroundingsaid portion, stay wires secured to the clamp for supporting the control member, and means comprising a member positioned in close proximity to said clamping device for preventing the initiation of induced heating currents when high frequency oscillations are generated in said reentrant portion, said member constituting a flat metallic plate secured to said stay wires.

2. In an electron discharge device, an evacuated envelope composed of a material which upon being heated conducts current to an appreciable extent, said envelope containing an electron emitting cathode, a control member, an anode, and having a reentrant portion, a. clamp embracing said reentrant portion for supporting the control member, said clamp constituting an intense source of electrostatic field when high frequency oscillations are imparted to the device whereby the glass of the reentrant por tion is subject to fracture, and means comprising a member positioned in close proximity to said clamp, for preventing the initiation of electric forces which cause fracture of the reentrant portion.

3. In an electron discharge device, an evacuated envelope composed of a material which upon being heated conducts current to an appreciable extent, said envelope containing an electron emitting cathode, a control member, an anode, and having a reenquency oscillations are imparted to the device whereby the glass of the reentrant portion is subject to fracture, and means comprising a member positioned in close prox- 5 imity to said clamp, for preventing the initiation of induced heating currents when high frequency oscillations are imparted to the device whereby the glass of the reentrant portion is precluded from failure.

4. In an electron discharge device, an evacuated envelope composed of a, material which upon being heated conducts current to an appreciable extent, said envelope containing an electron emitting cathode, a control member, an anode, and having a reentrant portion, a clamp embracing said reentrant portion for supporting the control member, and means comprising a member positioned in close proximity to said clamp for maintaining the reentrant portion relatively cool and for minimizing the deleterious effect of currents induced in said portion when high frequency oscillations are imparted to the device.

In witness whereof, I have hereunto set my hand this 29th day of June 1928.

MARCUS A. ACHESON. 

